Solid detergents are sometimes provided in "cast" or block form, wherein the detergent is cast within a sturdy, plastic container. The container acts as a mold, a shipping and storage container, and a dispenser housing. Dispensing systems for these solids are known in the art. See, for example, U.S. Pat. No. 4,426,362, issued to Copeland et al and commonly owned U.S. Pat. Nos. 4,569,781 and 4,569,780, issued Feb. 11, 1986, to Fernholz et al. The cast detergent is dispensed by spraying a solvent onto the detergent block within the container, thereby dissolving the exposed surface of the detergent to form a concentrated working solution. The concentrated working solution falls into a reservoir or is directed by a conduit to the wash tank of a washing apparatus. When the chemical compound within the capsule is completely utilized, the exhausted capsule is simply discarded and a fully charged container placed in the dispenser. However, hazardous chemicals used in cleaning processes such as highly alkaline detergents are preferably packaged such that they can be dispensed without coming into physical contact with the human body.
A difficulty with the above type of dispenser is that there is no simple way to determine when the capsule is empty and needs to be replaced. In practice, the user must remove the plastic capsule from the dispensing apparatus and visually check the amount of detergent remaining. Alternatively, an automatic detergent sensor may be employed, such as a conductivity sensor to measure the level of detergent in the cleaning solution. However, such a system is relatively expensive, often has high maintenance requirements, and requires auxiliary equipment and electrical circuitry.
Accordingly, a need exists for a dispensing apparatus for a solid block of wash chemical, including a simple, safe, efficient and inexpensive indicator for determining the level of solid detergent remaining in the container and for determining the appropriate time for an empty container to be replaced with a full container.